Science is running a special section on The Science of Inequality. Appropriately, all the articles are open access. Among them is this article by Thomas Piketty and Emmanuel Saez: Inequality in the long run. The abstract:
This Review presents basic facts regarding the long-run evolution of income and wealth inequality in Europe and the United States. Income and wealth inequality was very high a century ago, particularly in Europe, but dropped dramatically in the first half of the 20th century. Income inequality has surged back in the United States since the 1970s so that the United States is much more unequal than Europe today. We discuss possible interpretations and lessons for the future.